At roads, there are posted traffic signs indicative of information about a speed limit, a parking prohibition and the like. Although a passenger in a vehicle visually recognizes these traffic signs, because of having to turn his/her sight line to each traffic sign, the passenger often overlooks the traffic sign. In order to allow the passenger, when overlooked such a traffic sign, to confirm the overlooked traffic sign, there has been invented such a technology in which a road front-scenery image is acquired by a camera mounted on the vehicle, and a traffic sign is recognized from the acquired image and is then displayed on a display (for example, Patent Document 1).